BDNF and diabetic neuropathy: Skin levels of neurotrophins have been assessed in very few studies with somewhat contradictory results, with depletion of skin NGF in patients with diabetic neuropathy [9], and also increased NGF mRNA [17], neurotrophin-3 (NTF3) concentration [32], and expression of the trkA and trkC receptors for NGF and NTF3, respectively [33].